1. Field
Embodiments of the invention relate to the field of camera lens modules; and more specifically, to a camera module for use in portable digital devices.
2. Background
Many portable electronic devices, such as mobile cellular telephones, include a digital camera. The lenses for such cameras must be compact to fit within the case of the portable electronic device. At the same time there is a desire to provide an increasingly high quality camera function in these devices. To provide a higher quality image, some cameras found in portable electronic devices provide an autofocus feature.
The lens may be mounted in a mechanism that moves the lens along its optical axis to change the distance between the lens and the image sensor. This changes the focal distance of the camera and allows a sharper image to be obtained for subjects over a greater range of distances from the camera. One such lens moving mechanism for moving a lens is a voice coil motor (VCM). Typically a lens is inserted into a lens moving mechanism, such as a VCM, and an image sensor is then assembled to the lens moving mechanism to provide a camera lens module.
The lens moving mechanism generally includes a plurality of datum surfaces at an end of the mechanism closest to the image sensor. The datum surfaces of the lens moving mechanism may contact a similar plurality of datum surfaces on a fixed portion of the camera module body at a known distance from the surface of an image sensor where the lens focuses distant objects on the image sensor. This provides a reference position for an autofocus mechanism that moves the lens into focus for near objects using the VCM. The tolerance for the positioning provided by the datums is around 50 microns (0.05 millimeters, 0.002 inches). The parts are typically formed from a hard plastic to provide the necessary dimensional stability for the datums.
The lens moving mechanism is generally held with the datums in contact by a spring when the VCM is unpowered. The VCM moves the lens through a range of motion against the spring force when the VCM is powered. It is desirable to minimize the force that the VCM must provide to overcome the force provided by the spring. Generally the spring is chosen to be just sufficient to hold the datums in contact when the camera is pointed down. In other words, the spring is just sufficient to support the weight of the moving portion of the VCM, including the lens, against the force of gravity. As result mechanical shocks and vibrations can move the lens moving mechanism when the VCM is unpowered sufficiently to cause the datum surfaces of the lens moving mechanism to separate and then make contact. This contact may produce an audible sound, such as a click. If the camera module is used in a mobile device, such as a cellular telephone, the clicking of the datum surfaces due to mechanical shocks may be disturbing when the mobile device is close to an ear of a user.
It would be desirable to provide a datum surface for a camera module that reduces the sound created when a mechanical shock causes datum surfaces to contact one another while providing the necessary dimensional tolerance and stability.